The present invention relates in general to caster assemblies which employ a self-laying track member mounted in a bearing block for rotation about an inclined axis. Several devices of this type have previously been provided. U.S. Pat. No. 4,034,436 discloses a caster composed of a bearing block, a caster roller mounted in the bearing block for rotation about a horizontal axis, and a track member journaled in the bearing block for rotation about an inclined axis. The patents to Laugham (U.S. Pat. No. 2,810,151 and No. 3,928,888) show a caster employing a dished disk journaled in a bearing block on an inclined axis, the dished disk being provided with an inner track on which a wheel or roller rolls, while the outer surface of the inclined disk contacts the ground. It is pointed out that such devices are advantageous in facilitating the movement of a frame or other structure over carpeted and rough surfaces, due to the inclination of the track member producing a relatively large `footprint` in the surface on which it moves.
While investigations have focused primarily on the problems of the basic geometry of the caster, including the angle of inclination of the track member and the location of the swivel stem for optimum tracking ability, these problems and others have generally been inadequately dealt with. U.S. Pat. No. 392,888 for example, shows the location of the swivel stem within a range of positions which would cause the caster to drag rather than to roll over a smooth surface. In addition, such devices fail to deal adequately with the problem of stress in the track member and other components created during normal operation of the caster. It is to be pointed out that in such devices, the arrangement of the track member, caster roller, and bearing block is designed to support a load bearing generally on a single point on the track member and along a vertical line passing through the bearing point. In fact, in any but ideal conditions, the actual forces acting on the caster during normal operation are multi-directional. Particularly in applications where movement is required on rough or uneven surfaces, excessive stress would be placed on the track member and the spindle, causing misalignment of the axis of rotation, and rubbing of the edges of the track member and bearing block. In extreme situations, such stresses will cause premature failure of the caster.
The present invention is directed to overcoming the problems of stress produced by multi-directional forces acting on the caster during normal operation, and particularly such stress as produced when the caster moves on surfaces containing cracks, expansion joints, door sills, the edges of carpets, and other surface irregularities such as are commonly found in many industrial, institutional, and domestic settings.